Executive summary

APIs are essential for modern applications but also pose unique security risks. In this blog, we break down a typical API attack, exploring how attackers exploit vulnerabilities like Broken Object Level Authorization (BOLA), injection, and rate limiting issues. Through detailed examples, we show how these attacks work and the steps organizations can take to defend against them. With strong authentication, input validation, rate limiting, and continuous monitoring, businesses can secure their APIs against a range of threats and protect critical data and systems.

APIs have become a backbone for modern applications, enabling seamless communication between different services and devices. However, they’re also a prime target for cyber attackers, who exploit API vulnerabilities to gain unauthorized access, exfiltrate data, or disrupt services. In this blog, we’ll walk through the anatomy of a typical API attack, exploring how it unfolds technically and what steps can be taken to defend against it.

Understanding the API Vulnerability

APIs expose endpoints, and each endpoint becomes a potential attack surface. Suppose we have an API endpoint that’s poorly secured—for example, it might lack rate limiting or proper authentication. Attackers can exploit these vulnerabilities using various techniques such as Broken Object Level Authorization (BOLA) or mass assignment vulnerabilities.

Let’s consider an example: a financial services API that lets customers check their account balances by sending a request to an endpoint like /api/v1/accounts/{accountId}/balance. If this API does not implement strong authorization checks, an attacker can manipulate the accountId parameter to access data from another user’s account simply by modifying the request.

Step 1: Reconnaissance and Endpoint Discovery

The attack often begins with reconnaissance. An attacker might start by studying the API documentation (if publicly available) or using automated tools like Burp Suite or Postman to explore the endpoints. They may test endpoints with different parameter values, inspecting responses for clues about how the API is structured. Sometimes, APIs unintentionally expose sensitive details in error messages, which attackers can leverage to understand the system better.

Step 2: Exploiting BOLA

With a working knowledge of the endpoint, the attacker may next attempt a Broken Object Level Authorization (BOLA) attack. This technique targets improper access controls by manipulating object identifiers.

Here’s how it might work:

• The attacker authenticates as a legitimate user and receives their own account balance at /api/v1/accounts/1234/balance.
• Noticing that changing 1234 in the URL returns data for a different account, they replace it with another identifier, like 5678, and access someone else’s balance.

This type of attack succeeds if the API is not validating that the user requesting the data owns the accountId being accessed. As simple as this seems, BOLA attacks are among the most common API vulnerabilities due to inconsistent authorization checks.

Step 3: Injection Attacks Through API Requests

APIs often accept data in JSON, XML, or other structured formats, which can be manipulated to carry malicious payloads. If the API doesn’t sanitize input, attackers can perform SQL Injection, Command Injection, or Cross-Site Scripting (XSS) attacks.

Consider a login endpoint vulnerable to SQL injection:

POST /api/v1/login
{
    "username": "admin'--",
    "password": "password123"
}

If the API uses dynamic SQL without proper input sanitization, an attacker could craft a query that bypasses authentication. By manipulating the input, they might force the API to execute unintended SQL commands, potentially leading to unauthorized access or data exfiltration.

Step 4: API Abuse Through Rate Limiting Exploits

Attackers also exploit APIs without proper rate limiting by spamming requests to overwhelm the system, commonly known as API Abuse or Denial of Service (DoS). Without rate limiting, an attacker can send thousands of requests per second to endpoints that consume resources heavily—such as a search or reporting endpoint—eventually causing the API server to crash or become unresponsive.

For example:

curl -X GET "<https://api.example.com/v1/search?query=expensiveOperation>" -H "Authorization: Bearer attacker_token"

A botnet or automated script could send this request repeatedly until the API fails to respond.

Defense Strategies to Protect APIs

Securing APIs requires multiple layers of defense, and the following strategies can significantly reduce the risk of exploitation:

• Strong Authentication and Authorization: Implement OAuth, JWTs, or other token-based authentication mechanisms, ensuring that every request is verified. For authorization, adopt granular policies to ensure that users can only access resources they are permitted to view.
• Input Validation and Sanitization: Never trust client-supplied data. Use parameterized queries to prevent injection attacks and filter out any malicious input before processing it.
• Rate Limiting and Throttling: Set limits on the number of requests a user can make within a specific timeframe. API gateways like AWS API Gateway or tools like Kong can enforce rate limits, blocking users who exceed them.
• Implementing Object-Level Authorization Checks: Always verify that the user requesting an object has permission to access it. This can prevent BOLA attacks by ensuring user access is tightly controlled and monitored.
• Logging and Monitoring: Track API usage and monitor for unusual patterns. Automated detection tools can flag suspicious activity, alerting security teams to potential attacks before they escalate.

Conclusion

APIs are powerful tools that enable modern applications to deliver dynamic and interactive experiences. However, they also expand the attack surface, making it essential for developers and security teams to understand the methods attackers use and how to protect against them. By implementing strong authentication, input validation, rate limiting, and monitoring, organizations can secure their APIs against common attack techniques, ensuring that their data and users remain safe in an increasingly interconnected digital world.

Turn-key E2E API protection in hostile environments with Codesealer

Codesealer’s innovative approach makes secure E2E API Encryption between your web application and backend feasible. Our client-side Bootloader ensures that the E2E tunnel is safely established even in hostile environments, preventing the app code from being manipulated or reverse-engineered. By securing the communication channel from the browser to the backend, we protect the integrity and confidentiality of the data throughout its journey.

Codesealer’s solution involves multiple layers of security. The Bootloader verifies the integrity of the application code before it is executed, ensuring that no unauthorized modifications have been made. Once the application is running, it establishes a secure E2E tunnel that encrypts all data, making it inaccessible to attackers. This approach not only protects against API attacks but also enhances overall security by ensuring that the application code and data remain secure.

Ready to fortify your web applications against API attacks? Contact us today to learn how Codesealer can provide the proactive protection your business needs. Our cutting-edge technology ensures that your APIs remain secure, protecting your business from the ever-evolving threat landscape.

Contact us today to learn how Codesealer can provide the proactive protection your business needs. Our cutting-edge technology ensures that your APIs remain secure, protecting your business from the ever-evolving threat landscape.